Environmental and other concerns have increased the demand for oxygenated fuels components for internal combustion engines. For instance, methyl tert-butyl ether (MTBE), tert-amyl methyl ether (TAME) as well as ethyl tert-butyl ether (ETBE) are some potential high octane oxygenates for gasoline engines. This increases the demand for isobutylene, for MTBE and ETBE production, and 2-methyl butylene for TAME production. These olefins can be derived by dehydrating isobutanol and 2-methyl butanol, respectively.
Catalysts, based on zirconium oxide for the conversion of synthesis gas to the foregoing alcohols, but not for the production of isobutanol from methanol-ethanol mixtures, are disclosed in W. Keim and W. Falter, Catalysis Letters, Vol. 3, pp. 59-64, 1989 and M. Roper, W. Keim and J. Seibring, Federal Republic of Germany Patent Application No. 3,524,317A1. However, it is not always practical to convert synthesis gas directly to these alcohols. Instead it is often desirable to convert a mixture of methanol and ethanol in the presence of synthesis gas to isobutanol and 2-methyl butanol and other similar methyl branched alcohols.
Other catalysts, such as gamma alumina impregnated with an inorganic base promoters such as a basic metal salt and a Group VIII metal, are disclosed for example in U.S. Pat. No. 3,972,952 for the vapor phase conversion of methanol and ethanol to higher linear primary alcohols, for instance, n-butanol and n-propanol but not significant levels of isobutanol and 2-methyl butanol.
U.S. Pat. No. 4,681,868 and U.S. Pat. No. 4,935,538 discloses that copper bismuth mixed metal oxide catalyst promoted with alkali couples n-propanol to C.sub.6 aldol products but does not disclose the conversion of methanol/ethanol mixtures to isobutanol and 2-methyl butanol. U.S. Pat. No. 5,095,156 discloses that methanol and higher alcohols are coupled in the presence of magnesia, (MgO), and also discloses losses to methane, e.g., the weight % (wt %) selectivity of the water-free products in Table 7 of the patent shows a selectivity to CO and CO.sub.2 ranging from 35.8% to 67.7% and selectivity to methane ranging from 6.9% to 12.6% where methanol conversion ranged from 7.6% to 90.6% and ethanol conversion ranged from 20.4% to 99.1%. Such reactions are also discussed by W. Ueda et al. in Catalysis Letters, Volume 12, pages 97 to 104, 1992, although Ueda gives no information of losses to methane.